1. Field of the Invention
The present invention relates to an organic electroluminescent device having excellent light-emitting properties.
2. Description of Related Art
An organic electroluminescent device (which will hereinafter be called xe2x80x9corganic EL device) is a light-emitting device which makes use of the principle that when an electric field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode. After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, Vol. 51, 913 (1987) and the like), studies on an organic EL device have been briskly carried out. Tang et al. reported an organic EL device using tris(8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; blocking of electrons injected from a cathode, which increase the efficiency of exciton production from charge recombination; and confinement of the excitons into the light-emitting layer. A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices.
As a hole transport material, aromatic diamine derivatives such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine are well known(for example, Patent Publications JP-A-8-20771, JP-A-8-40995, JP-A-8-40997, JP-A-8-53397, and JP-A-8-87122).
As an electron transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
As a light-emitting material, known are chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like. Since various color light in a visible region from blue to red are obtained from these light-emitting materials, there is increased expectation for industrialization of a full color organic EL device (refer to, e.g., JP-A-8-239655, JP-A-7-138561, and JP-A-3-200889).
In recent days, organic EL devices with high brightness and long lifetime have been disclosed or reported, but any of them are not enough in these properties.
An object of the present invention is to provide a material of high performance and to provide an organic EL device having high luminance.
The present inventors have repeated experiments. As a result, they have found that an organic EL device having superior emission properties is obtained by using a specific diaryl, triaryl or tetra aryl compound which is substituted by diarylamino groups as a light-emitting material. They have found that said compound has high carrier transporting properties and an organic EL device having superior emission properties is obtained by using said compound as a hole-transporting material or electron-transporting material. They have found that an organic EL device having superior emission properties is obtained by using a mixture of said compound and another hole or electron-transporting material. They have found that an organic EL device having superior emission properties is obtained by using said diarylamino substituted compound which is substituted by styryl groups as an light-emitting material, hole-transporting material or electron-transporting material.
In the present invention, there is thus provided an organic EL device defined as follows:
(a) An organic EL device comprising an anode, a cathode and one or more than one organic thin-film layers including a light-emitting layer between said anode and said cathode, wherein at least one of said organic thin-film layers contains, either singly or as a mixture, a compound represented by the following formulas (1), (2) or (3): 
wherein Ar1, Ar1xe2x80x2 and Ar2 each represents any groups represented by following formulas (4), (5) and (6), and wherein Ar1 and Ar1xe2x80x2 are different from each other, 
wherein Ar3 and Ar4 each independently represents divalent group represented by following formulas (7) to (11), 
wherein R1 to R14 represent each independently a hydrogen atom, a halogen atom, a nitro group, a cyano group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group excluding a substituted or unsubstituted styryl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxycarbonyl group or a carboxyl group; and each pair of two of R1 to R3, R5-R6, R7-R8, R9-R10, and R13-R14 may form a ring. A1 to A13 represent an atomic group forming a substituted or unsubstituted condensed hydrocarbon ring, or a substituted or unsubstituted condensed heterocyclic ring. At least one among the substitutive groups R1 to R14 or ones existing in the ring structures represented by A1 to A13 is diarylamino group represented as xe2x80x94NAr5Ar6 (Ar5 and Ar6 each independently represents a substituted or unsubstituted aryl group having 6-20 carbon atoms (The carbon atoms of substituent groups are not counted.);
(b) An organic EL device defined in (a), wherein the organic thin-film layer includes at least a light-emitting layer which contains, either singly or as a mixture, a said compound;
(c) An organic EL device defined in (a), wherein the organic thin-film layer includes at least a hole-transporting layer which contains, either singly or as a mixture, a said compound;
(d) An organic EL device defined in (a), wherein the organic thin-film layer includes at least a electron-transporting layer which contains, either singly or as a mixture, a said compound;
(e) An organic EL device defined in (a), wherein the organic thin-film layer which contains, either singly or as a mixture, a said compound, and wherein the compound is such that at least one of Ar5 and Ar6 has a substituted or unsubstituted styryl group as a substituent group;
(f) An organic EL device defined in (e), wherein the organic thin-film layer includes at least a light-emitting layer which contains, either singly or as a mixture, a said compound;
(g) An organic EL device defined in (e), wherein the organic thin-film layer includes at least a hole-transporting layer which contains, either singly or as a mixture, a said compound; and
(h) An organic EL device defined in (c), wherein the organic thin-film layer includes at least a electron-transporting layer which contains, either singly or as a mixture, a said compound.
The EL device according to the present invention emits light with higher brightness compared with the conventional organic EL device.